A plated layer such as galvanized coating, hot-dip aluminum coating, hot-dip zinc-aluminum alloy coating or the like develops excellent rust proof power and corrosion proof power, so that it is a surface treated coating used as a member for automobile, aircraft, vehicle, building, household electrical articles and the like.
Among them, the galvanized steel sheets are generally produced by subjecting a surface of a steel sheet to a galvanizing treatment in a continuous galvanizing apparatus. In the continuous galvanizing apparatus are used members for molten metal bath such as a sink roll immersed in a plating bath, a support roll arranged near to the surface of the plating bath, guide rolls for guiding a plated steel sheet passed through these rolls and so on. These members are immersed in a plating bath, or placed in a place to easily be adhered with scattered hot-dip zinc and also used so as to contact with a high temperature steel sheet adhered with the hot-dip zinc, so that they are required to have the following properties.
(1) It is difficult to cause penetration through hot-dip zinc; PA0 (2) It is difficult to cause wearing even when being contacted with a passing plate (steel sheet); PA0 (3) The peeling of the hot-dip zinc adhered and the inspection for maintenance are easy; PA0 (4) The life as a member for plating is long and the cost is low; PA0 (5) It is sufficiently durable to thermal shock in the immersion in to a high-temperature hot-dip zinc bath. PA0 (1) In the spray coatings formed in air, pores are present and also oxides are incorporated therein. Therefore, even if the spray coating material is a substance not causing the metallurgical reaction with molten metal, the molten metal passing through the pore portion penetrates into the inside of the coating and reacts with a matrix metal to peel and break the coating from its base. PA0 (2) Since a metal having a small oxide-forming energy as in molten aluminum reduces an oxide included in the coating (the spraying material is oxidized in a spray heating source and retained in the coating as it is), the pore is enlarged and the metallurgical reaction with the metal formed by reduction is caused to change the volume and break the coating. PA0 (3) The carbide cermet exemplified by WC--Co or the like is used as a spray coating for a anti-fusion metal. However, molten metal adheres to a metal component included in the coating or metallurgically reacts therewith to promote the sticking of dross component and finally lower the quality of the plated steel sheet. PA0 (4) The spray coated members used in a molten metal bath are required to have a heat resistance and a strong resistance to thermal shock because they are used under a high-temperature environment. PA0 1. That is, the invention lies in a member provided with a composite coating, characterized in that a spry coating is formed on a surface of a steel base member as an undercoat and a vitreous coating is formed thereon as a topcoat and the spray coating has an oxide layer at its side facing the vitreous coating. PA0 2. In the invention, the spray coating formed as an undercoat is formed by spraying at least one or more spraying material selected from metals, oxide or non-oxide ceramics and their cermets. PA0 3. In the invention, the spray coating is a coating formed by subjecting the spraying materials alone or in admixture to spraying in form of one layer or plural layers. PA0 4. In the invention, the spray coating of the plural layers has a structure of two or more layers by spraying different spraying materials. PA0 5. In the invention, the spray coating has a thickness of 10-750 .mu.m. PA0 6. In the invention, the oxide layer formed on the surface side of the spray coating has a thickness of not less than 0.5 .mu.m. PA0 7. In the invention, the vitreous coating formed as a topcoat is formed by heating a vitreous starting material consisting essentially of one or more glass-forming oxides selected from SiO.sub.2, Na.sub.2 O, K.sub.2 O, BaO, B.sub.2 O.sub.3, MgO, CaO, PbO, CoO, MnO.sub.2, NiO, TiO.sub.2 and ZnO and glass ceramics and porcelain enamel, or immersing into a bath of these molten vitreous starting materials. PA0 8. A member provided with a composite coating according to claim 1, wherein the vitreous coating has a linear expansion coefficient of 4-11.times.10.sup.-6 /.degree.C. PA0 9. A method of producing am ember provided with a composite coating excellent corrosion resistance and resistance to molten metal, characterized in that at least one spraying material selected from metals, ceramics and cermets thereof is sprayed alone or in admixture onto a surface of a steel base member in form of a one layer or plural layers to form a spray coating, and then a vitreous starting material is applied onto the surface of the spray coating and is fired at 500-1000.degree. C. for 0.5-10 hours or immersed in a bath of molten vitreous starting material and fired to form a vitreous coating and is composited with the spray coating. PA0 10. In the invention, the spray coating as an undercoat is formed by spraying different spraying materials to form two or more layers. PA0 11. In the invention, after the formation of the spray coating, an oxide layer is formed on the surface of the spray coating by heating the coating. PA0 1 as a metal material, there are Ni, Fe, Mo, Cr, Co, Ti, Nb, Si, Al, W and alloys thereof; PA0 2 as a ceramic material, there are the following one ceramic or a mixture of two or more ceramics; PA0 3 as a cermet material, there is a mixed powder or sintered powder of the metal material of the item 1 and the ceramic material of the item 2. PA0 (a) After Ni(80)-Cr(20) alloy was sprayed onto a surface of a test piece of SUS 430L (ferritic stainless steel) in an atmosphere of Ar gas substantially containing no air, powder of frit having a composition of 1 wt % K.sub.2 O-8 wt % Na.sub.2 O-1 wt % CoO-2 wt % NiO-5 wt % B.sub.2 O.sub.3 -83 wt % SiO.sub.2 was applied thereonto and fired at 900.degree..times.1 hour to form a composite coating. PA0 (b) After Ni(80)-Cr(20) alloy was sprayed in air, the same frit powder as in the item (a) was fired to form a composite coating. PA0 (c) After 73 wt % Cr.sub.3 Cr.sub.2 -20 wt % Ni-7 wt % Cr was sprayed in air, the same frit powder as in the item (a) was fired to form a composite coating. PA0 (d) After 100 wt % TiN was sprayed in air, the same frit powder as in the item (a) was fired to form a composite coating. PA0 (e) After 80 wt % Ni-19 wt % Cr-0.5 wt % Al-0.5 wt % Si was sprayed in air, the resulting spray coating was subjected to a heating treatment at 500.degree. C..times.15 minutes and the same frit powder as in the item (a) was fired thereon to form a composite coating. PA0 (1) it consists essentially of vitreous one: Na.sub.2 O, K.sub.2 O, BaO, B.sub.2 O.sub.3, SiO.sub.2, MgO, CaO, PbO PA0 (2) it consists essentially of SiO.sub.2, Al.sub.2 O.sub.3, B.sub.2 O.sub.3, CaF, Na.sub.2 O, K.sub.2 O using a porcelain starting material such as natural feldspar, natural silica, soda ash (Na.sub.2 CO.sub.3), boride sand (Na.sub.2 B.sub.2 O.sub.7) or the like and contains CoO, MnO, NiO, TiO.sub.2, ZnO or the like as a slight component.
In order to satisfy the above requirements, taking a coating for sink roll, there are proposed the followings:
(1) the formation of a coating having an alloy composition according to Co-based self-fluxing alloy defined in JIS H8303(1976) as disclosed in JP-B-56-39709, JP-B-58-11507, JP-A-59-153875, JP-A-1-108334, JP-A-64-79356 and JP-A-2-125833; PA1 (2) the formation of spray coating of oxide ceramics comprising ZrO.sub.2 and Al.sub.2 O.sub.3 as disclosed in JP-A-61-117260, JP-B-3-54181 and JP-B-4-27290; PA1 (3) the formation of cermet spray coating in which a metal such as Cr, Ni, Co or the like is co-existent in a non-oxide ceramics such as carbide, nitride, boride or the like as disclosed in JP-B-58-37386, JP-A-2-212366, JP-A-2-180755, JP-A-3-94048, JP-A-4-13857 and JP-A-4-346640; PA1 (4) a combination of techniques of the above items (1) and (3) as disclosed in JP-A-4-13857; PA1 (5) overlaying of anti-fusion metal disclosed in JP-B-52-22934, spray coating of W disclosed in JP-A-53-128538, spray coating of Cr disclosed in JP-A-165058 and the like. PA1 (6) spray coating of WC cermet containing 5-28% of Co and having a porosity of not more than 1.8% and a thickness of 0.040-less than 0.10 mm in Japanese Patent Application No. 63-49846 (JP-A-1-225761); PA1 (7) a technique of subjecting boride or a boride material containing 5-28% of Co to a plasma spraying under a reduced pressure in Japanese Patent Application No. 63-192753 (JP-A-2-43352); PA1 (8) the formation of a coating having a surface roughness Ra of 0.01-5 .mu.m and a porosity of not more than 1.8% by subjecting a material of ZrB.sub.2, TiB.sub.2 or various carbides containing 5-40% of Ta, Nb to a plasma spraying under a reduce pressure in Japanese Patent Application 1-54883 (JP-A-2-236266); PA1 (9) a coating obtained by forming Cr.sub.3 O.sub.3 onto a cermet spray coating consisting essentially of a carbide through chemical densification method in Japanese Utility Model Application No. 1-124010 (JP-Y-3-63565); PA1 (10) a coating in which a part of a carbide spray coating is changed into a boride through boridation treatment in Japanese Patent Application No. 2-201187 (JP-A-4-88159); PA1 (11) the improvement of resistance hot-dip zinc by diffusing Al or Al--Zn alloy into various carbides, borides or their cermet spray coatings under heating in Japanese Patent Application No. 3-31448 (JP-A-4-254571); PA1 (12) a diffusion penetration of Al or Al--Zn alloy into non-oxide ceramic spray coating in Japanese Patent Application No. 3-31448 (JP-A-4-254571); PA1 (13) a spray coating formed by using a spraying material constituted by adding Al or Al--Zn alloy to non-oxide ceramic powder or powder mixed with a metal in Japanese Patent Application No. 3-222425 (JP-A-4-358055); PA1 (14) a spray coating formed by using a spraying material constituted by adding Al--Fe alloy or Al--Fe--Zn alloy to non-oxide ceramic powder or powder mixed with a metal in Japanese Patent Application No. 3-213143 (JP-A-5-33113); PA1 (15) the formation of Al--Fe alloy layer having an Al content of not less than 22% on a surface of a steel roll in Japanese Patent Application No. 3-266874 (JP-A-5-78801). PA1 a. oxides such as Al.sub.2 O.sub.3, TiO.sub.2, MgO, ZrO.sub.2, Ta.sub.2 O.sub.5, Nb.sub.2 O.sub.5, SiO.sub.2 and the like; PA1 b. carbides such as WC, Cr.sub.3 C.sub.2, NbC, TaC, HfC, MoC, ZrC, TiC and the like; PA1 c. borides such as NiB.sub.2, CrB.sub.2, W.sub.2 B.sub.5, TiB.sub.2, ZrB.sub.2, NbB.sub.2, TaB.sub.2 and the like; PA1 d. nitrides such as TiN, VN, NbN, TaN, HfN, ZrN, BN, Si.sub.3 N.sub.4, CrN and the like; PA1 Composite coating (a) . . . local peeling at the repetition of 2 times PA1 Composite coatings (b), (c), (d), (e) . . . normal even at the repetition of 5 times PA1 Composite coating (b) . . . local peeling at the repetition of 7 times PA1 Composite coatings (c), (d), (e) . . . normal even at the repetition of 10 times
In connection with the above techniques, the inventors have studied and developed the same kind of the technique. For example, there are proposed the following techniques and coatings:
In this connection, the inventors have found that there are still the following problems to be solved as to the resistance to molten metal in the above spray coatings. That is,
It is a main object of the invention to provide members developing excellent effects when being applied to a member for anti-fusion metal, particularly members provided with a composite coating having excellent corrosion resistance and resistance to molten metal.
Further, it is another object of the invention to propose a structure of a composite coating being large in the resistance to peel or breakage of the coating and having excellent heat resistance and resistance to thermal shock.
It is the another object of the invention to solve the aforementioned problems and to provide members developing an excellent corrosion resistance to acid, alkali aqueous solution, molten salts such as chloride, sulfate, nitrate and the like and capable of being advantageously used under such corrosive environment.
It is a further object of the invention to provide a method of efficiently forming the above composite coating on a surface of a steel base member.